The present invention relates to image-recording elements and, more particularly, to color-providing compounds which, in the presence of silver ions and/or a soluble silver complex, undergo a cleavage reaction to liberate a color-providing moiety.
It is well known that various cleavage reactions are assisted by silver ions including reactions involving cleavage of a compound into one or more fragments. For example, U.S. Pat. No. 3,719,489 discloses silver ion assisted cleavage reactions useful in photographic systems. As disclosed therein, compounds are capable of undergoing cleavage in the presence of silver ions made available imagewise during processing of a silver halide emulsion to liberate a reagent, such as, a photographically active reagent comprising, for example, a color-providing compound, in an imagewise distribution corresponding to that of said silver ions. It is well known in the art that compounds useful for liberating a reagent include 1,3-sulfur-nitrogen compounds, e.g., thiazolidines, and their vinyl and phenylene analogs. In addition, U.S. Pat. No. 5,569,574 discloses the use of 1,3-sulfur-oxygen compounds in silver assisted cleavage reactions to liberate a reagent.
In one embodiment disclosed in U.S. Pat. No. 3,719,489, color images are produced by using as the compounds, color-providing compounds which are substantially non-diffusible in the photographic processing composition but capable of undergoing cleavage in the presence of the imagewise distribution of silver ions and/or soluble silver complex made available in the undeveloped and partially developed areas of a silver halide emulsion as a function of development to liberate a more mobile and diffusible color-providing moiety up in an imagewise distribution corresponding to the imagewise distribution of said ions and/or said complex. The subsequent formation of a color image is the result of the differential in diffusibility between the parent compound and liberated color-providing group whereby the imagewise distribution of the more diffusible color-providing moiety released in the undeveloped and partially developed areas is free to transfer.
Color-providing compounds useful in the above process form the subject matter of U.S. Pat. No. 4,098,783, a continuation in part of said U.S. Pat. No. 3,719,489. The color-providing compounds disclosed therein may include one or more dye radicals and one or more 1,3-sulfur-nitrogen moieties. For example, they may comprise one complete dye or dye intermediate and one cyclic 1,3-sulfur-nitrogen moiety. Alternatively, the color-providing compounds may comprise two or more cyclic moieties for each dye radical or dye intermediate or vice versa. In contrast, the dye-providing compounds of the present invention comprise two cyclic 1,3-sulfur-nitrogen moieties and one dye radical or dye intermediate. The presence of two cyclic moieties mandates that two silver ion assisted cleavage reactions occur prior to release of the dye or dye intermediate, thus, a desirable decrease in non-specific release of the dye or dye intermediate is effectuated. Furthermore, the presence of the solubilizing groups, e.g., --NHSO.sub.2, OH, on the dye-providing compound result in very rapid transfer of the dye or dye intermediate to the image-receiving element.
As stated earlier, the color-providing compounds according to the present invention are useful for forming color images in thermographic imaging systems processed by imagewise heating and in photographic imaging systems utilizing silver halide wherein the method of processing employs either wet processing to develop the image or thermal processing which develops the image by heating. Of particular interest are the integral-type film configuration photographic imaging systems utilizing silver halide and employing wet processing.
Color photosensitive imaging materials are well known in the art. Further, it is known in the art that such imaging materials may include various image dye-providing materials to provide the desired image. For example, Japanese Kokai 59-180548 having a Laid-Open date of Oct. 13, 1984 discloses a heat-developable silver halide photosensitive imaging system wherein the dye-providing material contains a heterocyclic ring containing a nitrogen atom and a sulfur or selenium atom which heterocyclic ring is subject to cleavage in the presence of silver ions to release a diffusible dye.
As mentioned above, an example of a suitable dye-providing material is a thiazolidine dye such as disclosed in U.S. Pat. No. 4,098,783. The process involves imagewise exposing the photosensitive system to light and subsequently or simultaneously heating the photosensitive system, in the presence of a base or base precursor, under a substantially water-free condition whereby an oxidation-reduction reaction between the exposed photosensitive silver halide and a reducing agent occurs. In the exposed areas, a negative silver image is formed. In the unexposed areas, the silver ion, present in inverse proportion to the silver image, causes the heterocyclic ring of the dye-providing material to be cleaved, releasing a diffusible dye. The diffusible dye is then transferred to an image-receiving layer, whereby a positive dye image is formed.
However, while the differential in diffusibility between the parent compound and the liberated color-providing moiety, disclosed in U.S. Pat. No. 3,719,489, is useful in obtaining a color image, under some conditions a small amount of the parent compound may also transfer. One way to lessen the diffusion of uncleaved dye-providing material is to use additional dye providing radicals as ballast groups. Another way to lessen the diffusion of uncleaved dye-providing material is to add additional ballasting groups and/or to increase the size of the ballast groups. U.S. Pat. No. 5,320,929 teaches the decrease in diffusion of particular color-providing compounds by using additional color-providing radicals, e.g., cyclic 1,3-sulfur-nitrogen moieties, and/or ballast groups. U.S. Pat. No. 5,415,970 discloses additional dye providing radicals as ballast groups to decrease diffusion of the uncleaved parent compound to the receptive layer of the film unit while increasing the image-forming efficiency of the color-providing materials, i.e., releasing more dye-providing moieties per molecule of uncleaved color-providing material. However, while these techniques do lessen such diffusion of the uncleaved parent compound to the receptive layer of the film unit, the results obtained are not entirely satisfying.
As the state of the art advances, novel approaches continue to be sought in order to attain the required performance criteria for these photographic systems. The present invention relates to dye-providing compounds.